Motor vehicle comprising a hybrid drive and method for controlling the idle speed of a hybrid drive of a motor vehicle

ABSTRACT

A motor vehicle having a hybrid drive and a method for idle-speed control of a hybrid drive of a motor vehicle are provided. The hybrid drive includes an internal combustion engine having an engine management system, and at least one speed-controlled electric machine which is coupled to a drive shaft of the internal combustion engine during idling. During idling, the internal combustion engine is controlled by the engine management system in open or closed loop as a function of power demands of an electrical system of the motor vehicle.

FIELD OF THE INVENTION

The present invention relates to a motor vehicle having a hybrid driveand to a method for idle-speed control of a hybrid drive of a motorvehicle.

BACKGROUND INFORMATION

Motor vehicles having a hybrid drive include, in addition to aconventional internal combustion engine, one or possibly more associatedelectric machines that are able to be coupled or fixedly connected to adrive shaft in the drive train of the motor vehicle and able to operateboth in generator mode and in motor mode. When in generator mode, theelectric machines are driven by the internal combustion engine and areable to generate electric current to supply loads of the motor vehicle,whereas in the motor mode, the electric machines are supplied withcurrent from the vehicle battery to convert this current into motivepower for the motor vehicle or into starting power for the internalcombustion engine. In addition to the vehicle battery as a power storagedevice, a flywheel or a different kinetic energy storage device could beprovided, for example, to allow kinetic energy released during brakingto be stored and supplied to loads of the motor vehicle via the electricmachine, or to be supplied to the drive train thereof at a later time.

During speed-controlled idle operation of the internal combustionengine, the electric machine is automatically operated in generatormode.

In motor vehicles having a hybrid drive, the open and closed-loopcontrol tasks required for the operation of the internal combustionengine and the electric machine are generally distributed in the sameway as in conventional motor vehicles. This means that the control ofthe rotational speed of the internal combustion engine is assumed by theelectronic engine management system, which measures the speed andcalculates control variables, such as injection quantity, ignitionangle, or air quantity for the internal combustion engine, usingsuitable control methods so as to adjust or maintain the predeterminedidling speed. In contrast, the voltage regulation of a vehicleelectrical system and a charging control of a battery of the motorvehicle are accomplished in that power required by the vehicleelectrical system or for charging the battery is provided by theelectric machine with the aid of a controller of the electric machine.

However, the functions performed in the electronic engine managementsystem to control the speed of the internal combustion engine are verycomplex because the control can only be carried out at the moment ofignition of the internal combustion engine, which results in aidle-speed control that is moderately fast and more or less smooth,depending on the number of cylinders. Moreover, a relatively high degreeof complexity is necessary because the control must be stable under alloperating conditions and protected against numerous disturbances.

In contrast, the speed of an electric machine can be controlledrelatively easily and, moreover, torque control can be implemented withlittle effort and good results.

A motor vehicle having a hybrid drive and a method for idle-speedcontrol of a hybrid drive of a motor vehicle are described in publishedGerman Patent Application DE 195 32 163. The method is used to reducerotational irregularities of a shaft, in particular of the drive shaftof an internal combustion engine, and an electric machine coupled, orable to be coupled, to the drive shaft is controlled in such a mannerthat the rotational irregularities thereof are reduced. Moreover, due toits speed and performance, the controller responsible for controllingthe electric machine may also be used to perform engine managementtasks, including, for example, control of the speed of the internalcombustion engine during idling, while on the other hand, the enginemanagement system may assume one or more tasks of the controller of theelectric machine, such as control torque of the electric machine.

In this connection, however, problems may arise with respect to thepower demands of the electrical system of the motor vehicle because thevehicle electrical system must be subordinated to the requirements ofthe idle-speed control when the intention is to adjust and maintain apredetermined idling speed with the aid of the electric machine. If, forexample, immediately after the start of the motor vehicle when theinternal combustion engine is idling, an electrical load, such as arear-window heater, is switched on while at the same time a batterycharge controller of the motor vehicle requests current to be suppliedfor charging the vehicle battery, then the electric power required forthis from the electric machine cannot be provided immediately becausethis would in turn have negative effects on the control of the speed ofthe internal combustion engine.

SUMMARY

The motor vehicle having a hybrid drive and a method for idle-speedcontrol according to the present invention have the advantage over therelated art that the power demands of the vehicle electrical systemduring idling may be immediately and essentially fully met bycontrolling the internal combustion engine in open or closed loop as afunction of the requirements of the vehicle electrical system, withoutconsideration of the speed control. By substituting the speed controllerof the internal combustion engine by at least one speed-controlledelectric machine during idling, it is also possible to improve thecontrol performance and to reduce the extent of application of theidle-speed controller. Furthermore, a deactivated, engine-sideidle-speed controller allows a considerable reduction in fuelconsumption and exhaust gases.

In the context of the present patent invention, the electric powerrequested for charging a battery of the motor vehicle and optionallyalso the electric power consumed by the electrical loads of the motorvehicle at the same time are referred to as the power demands of thevehicle electrical system.

In an example embodiment of the present invention, the power output ofthe internal combustion engine is adjusted to the instantaneous powerdemand of the electrical system of the motor vehicle by ascertaining, asa function of the instantaneous power demand, a desired or setpointtorque of the internal combustion engine at which the electric poweroutput of the electric machine is approximately equivalent to the powerdemands of the vehicle electrical system.

The electric power that needs to be provided by the electric machine tomeet the power demands of the vehicle electrical system is taken as thebasis for ascertaining this desired or setpoint torque of the internalcombustion engine.

This necessary power mainly includes the electric power required tocharge the vehicle battery and the electric power consumed by theelectrical loads of the motor vehicle during idling.

The electric power required to charge the battery may be determined bymeasuring the battery voltage or, in accordance with an exampleembodiment of the present invention, in that, in addition to the batteryvoltage, the instantaneous state of charge of the battery is alsodetermined and included in the calculations for determining the electricpower required to charge the battery.

In order to determine the electric power required by the electricalloads of the motor vehicle during idling, it is possible to query theon-state of all possible loads and to add up the nominal power of theloads that are turned on at a time. Possible loads may be, for example,a rear-window heater or a seat heater of the motor vehicle, or parts ofthe lighting system, which are frequently turned on immediately afterstarting the motor vehicle while the vehicle is still idling, as well aselectrical control units of the motor vehicle that are automatically putinto operation when starting the motor vehicle and which requireelectric power during operation.

The electric power that is calculated from these parameters and whichneeds to be provided by the electric machine to meet the power demandsof the vehicle electrical system is subsequently converted to thedesired or setpoint torque of the internal combustion engine; a furtherinfluencing parameter, e.g., the current engine temperature and/or therotational speed of the internal combustion engine, may be taken intoaccount via a precontrol. Conveniently, the precontrol includes acharacteristics map to be applied, in which the aforementioned furtherinfluencing parameter is included. The precontrol ensures that ameasured power output of the electric machine driven by the internalcombustion engine is approximately equivalent to the calculated powerdemand.

Since, for the sake of simplification, it may not be useful to considerall possible influencing parameters in ascertaining the desired orsetpoint torque, and because minor deviations between the calculated andthe actual power output of the electric machine are to be expected,another example embodiment of the present invention provides to measurethe actual power output of the electric machine, and to determinepossible deviations between the measured and the calculated power bycomparing the two values, as well as to compensate for possibledeviations via a connected slow controller of the engine managementsystem or the control unit of the electric machine, by adjusting thedesired or setpoint torque of the internal combustion engine accordingto the result of the comparison.

In a Diesel engine, the adjustment of the desired or setpoint torque canbe accomplished by suitably varying the injection quantity, while in agasoline engine, it may be adjusted by suitably varying the airquantity, or optionally also by changing the ignition timing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic representation of a hybrid drive of a motorvehicle including an internal combustion engine and an electric machine.

FIG. 2 shows a signal flow diagram of an example embodiment of theidle-speed control of the hybrid drive.

DETAILED DESCRIPTION

The motor vehicle hybrid drive shown in FIG. 1 includes an internalcombustion engine 10, whose crankshaft 12 is able to be coupled via twogear wheels 14, 16 and a clutch 18 to the output shaft 20 of an electricmachine 22 of the motor vehicle.

Electric machine 22 has a control unit 24 and is connected via controlunit 24 to a battery 26 of the motor vehicle, and the battery suppliesDC current to a plurality of loads 28, 30, 32, etc., in an electricalsystem 34 of the motor vehicle. Loads 28, 30, 32 include allelectrically operated units of the motor vehicle, such as therear-window heater, the radio, the glow plug, and the individual lampsof the lighting system. Control unit 24 is also connected to an anglesensor 36 for determining the rotational speed of crankshaft 12.

Electric machine 22 serves as a starter-generator for internalcombustion engine 10. Each time the motor vehicle is started, theelectric machine is initially brought to a predetermined speed by thesupply of power from battery 26, whereupon clutch 18 is closed andinternal combustion engine 10 is started by electric machine 22 in atorque-controlled or speed-controlled manner. Once internal combustionengine 10 has reached a predetermined idling speed, control unit 24recognizes the end of starting by the signals from angle sensor 36.After that, internal combustion engine 10 is speed-controlled with theaid of electric machine 22 and control unit 24, the electric machine 22ensuring that the predetermined idling speed is maintained. Duringspeed-controlled idle operation, electric machine 22 automatically goesinto generator mode, in which it supplies current to battery 26.

Control unit 24 of electric machine 22 is equipped with a computer 38 towhich the on-state of the individual loads 28, 30, 32 of vehicleelectrical system 34 is transmitted by a central on-board computer 40 ofthe motor vehicle. Computer 38 further includes a memory 42, in whichthe nominal power values of the individual loads 28, 30, 32 are stored.Moreover, computer 38 is connected to a battery controller 44, whichdetermines the instantaneous terminal voltage and the instantaneousstate of charge of battery 26, and which ensures that battery 26 ischarged when necessary, for example, when the state of charge fallsbelow a level of 70%.

Based on the signals from on-board computer 40 and battery controller44, computer 38 determines, during idling, the current power demand forcharging battery 26 and the current power demand of turned-on loads 28,30, 32, which is obtained by adding up the nominal power values ofturned-on loads 28, 30, 32. This power demand during idling isessentially equivalent to the total power demand of vehicle electricalsystem 34 that needs to be provided by the electric machine whenoperating in generator mode.

Control unit 24 also includes a measuring device 46 for measuring thecurrent intensity of the electric current flowing from electric machine22 into the vehicle electrical system 34. The current intensity, inconjunction with the voltage of vehicle electrical system 34, allowscalculation of the actual power output from electric machine 22 intovehicle electrical system 34.

Internal combustion engine 10, which is designed as a Diesel engine, hasan engine management system 48 which, unlike in conventional internalcombustion engines, is not used to control the idling speed of internalcombustion engine 10, but to control the Diesel fuel injection quantityduring idling as a function of a desired or setpoint torque MWtransmitted by control unit 24 via a line 50 to engine management system48. When, during idling, internal combustion engine 10 isspeed-controlled by electric machine 22, the power output of electricmachine 22 may be controlled via this requested desired or setpointtorque MW and be adjusted to the instantaneous power demand of vehicleelectrical system 34.

As shown in FIG. 2, the requested desired or setpoint torque MW isascertained in that in a first step 100, the instantaneous total powerdemand of vehicle electrical system 34 is determined by computer 38 incontrol unit 24, as described above. The power that must be supplied byelectric machine 22 to the vehicle electrical system 34 to meet thispower demand is calculated from this total power demand in a second step101, taking into account a possible power loss. In a third step 102,this power demand is converted to desired or setpoint torque MW1 via aprecontrol 52. Precontrol 52 is essentially made of a characteristicsmap to be applied. The current engine temperature and, possibly, therotational speed of internal combustion engine 10 may be taken intoaccount as a further input variable E.

Desired or setpoint torque MW1 output by precontrol 52 is fed via line50 to engine management system 48, which then adjusts the Diesel fuelinjection quantity in such a manner that internal combustion engine 10delivers the desired or setpoint torque MW1 to crankshaft 12.

At this desired or setpoint torque MW1, the actual power output fromelectric machine 22 into vehicle electrical system 34 is essentiallyequivalent to the calculated power demand. In order to identify possibledeviations, if necessary, and to adjust the power output of electricmachine 22 even better to the power demand of vehicle electrical system34, the actual power output of electric machine is determined bycomputer 38 in a fourth step 104 with the aid of measuring device 46 andcompared, in a comparator circuit or using a suitable software ofcomputer 38, to the power output calculated in step 101.

In case of an upward or downward deviation, this deviation is correctedby a connected slow controller 54 in a fifth step 105 so that the outputvariable transferred by control unit 24 to engine management system 48is a desired or setpoint torque MW2 which, in accordance with thedeviation, is slightly greater or less than desired or setpoint torqueMW1. This slow control in step 105 operates with a response time ofseveral seconds during which the deviation is buffered by battery 26.

1. A hybrid drive system for a motor vehicle, comprising: an internalcombustion engine having a drive shaft and an engine management system;and at least one speed-controlled electric machine coupled to the driveshaft of the internal combustion engine during idling; means fordetermining overall power demands of an electrical system of the motorvehicle during idling, wherein the electrical system of the motorvehicle includes all electrically operated units of the motor vehicle; apre-control unit for converting the overall power demands of theelectrical system of the motor vehicle during idling into a setpointtorque of the internal combustion engine; wherein, during idling, theengine management system controls the internal combustion engine in oneof open and closed loop as a function of the overall power demands ofthe electrical system of the motor vehicle; wherein during idling theinternal combustion engine is speed-controlled with the aid of theelectric machine; wherein a power output of the internal combustionengine is adjusted to an instantaneous overall power demand of theelectrical system of the motor vehicle; and wherein the setpoint torqueof the internal combustion engine is determined as a function of theinstantaneous overall power demand of the electrical system of the motorvehicle, and at least one of an injection quantity, an air quantity, andan ignition angle of the internal combustion engine is adjustedaccording to the determined setpoint torque.
 2. The hybrid drive systemas recited in claim 1, wherein the means for determining the powerdemands of the electrical system of the motor vehicle during idlinginclude means for at least one of measuring a terminal voltage anddetermining a state of charge of a battery of the motor vehicle.
 3. Thehybrid drive system as recited in claim 1, wherein the means fordetermining the power demands of the electrical system of the motorvehicle during idling include means for detecting turned-on loadsassociated with the electrical system and calculating a nominal power ofthe turned-on loads.
 4. The hybrid drive system as recited in claim 1,further comprising: means for measuring a power output of the at leastone speed-controlled electric machine.
 5. The hybrid drive system asrecited in claim 4, wherein the means for determining the power demandsof the electrical system of the motor vehicle include a comparatordevice for comparing a power output of the at least one speed-controlledelectric machine calculated from the power demands of the electricalsystem and a measured power output of the at least one speed-controlledelectric machine.
 6. The hybrid drive system as recited in claim 5,further comprising: a slow controller for adjusting one of the desiredtorque and the setpoint torque of the internal combustion enginedepending on an output variable of the comparator device.
 7. A methodfor idle-speed control of a hybrid drive of a motor vehicle having aninternal combustion engine and at least one speed-controlled electricmachine, comprising: coupling the at least one speed-controlled electricmachine to a drive shaft of the internal combustion engine duringidling; and one of adjusting and maintaining a predetermined idlingspeed of the internal combustion engine during idling, with the aid ofthe at least one speed-controlled electric machine; wherein, duringidling, the internal combustion engine is controlled in one of open andclosed loop as a function of overall power demands of an electricalsystem of the motor vehicle with the aid of the engine managementsystem, and wherein the electrical system of the motor vehicle includesall electrically operated units of the motor vehicle; wherein a poweroutput of the internal combustion engine is adjusted to an instantaneousoverall power demand of the electrical system of the motor vehicle; andwherein a setpoint torque of the internal combustion engine isdetermined as a function of the instantaneous overall power demand ofthe electrical system of the motor vehicle, and at least one of aninjection quantity, an air quantity, and an ignition angle of theinternal combustion engine is adjusted according to the determinedsetpoint torque.
 8. The method as recited in claim 7, wherein a poweroutput of the at least one speed-controlled electric machine necessaryfor meeting the power demands of the electrical system of the motorvehicle is calculated and used to determine the setpoint torque of theinternal combustion engine.
 9. The method as recited in claim 7, whereinat least one of a terminal voltage and a state of charge of a battery ofthe motor vehicle is measured to determine the power demands of theelectrical system of the motor vehicle.
 10. The method as recited inclaim 7, wherein, to determine the power demands of the electricalsystem of the motor vehicle, turned-on loads associated with theelectrical system of the motor vehicle are detected and nominal powersof the turned-on loads are summed.
 11. The method as recited in claim 8,wherein the calculated power output of the at least one speed-controlledelectric machine is converted to one of a desired torque and thesetpoint torque using a pre-control unit.
 12. The method as recited inclaim 8, wherein an actual power output of the at least onespeed-controlled electric machine is measured and compared to thecalculated power output of the at least one speed-controlled electricmachine.
 13. The method as recited in claim 11, wherein the pre-controlunit includes a characteristics map to be applied, and wherein thepre-control unit takes into account at least one of an enginetemperature and a rotational speed of the internal combustion engine asa further input variable in the conversion of the calculated poweroutput to one of the desired torque and the setpoint torque.
 14. Themethod as recited in claim 12, wherein in case of a deviation of themeasured power output of the at least one speed-controlled electricmachine and the calculated power output of the at least onespeed-controlled electric machine, the setpoint torque is slowlyadjusted.